It is useful in both experimental and clinical applications to know whether cells are undergoing cellular death. Cells can undergo death by apoptosis or non-apoptotic cell death. Cell death plays a significant role in both normal and disease-related biological processes. Cells undergo apoptosis in response to a variety of stresses including chemotherapy, radiation therapy, photodynamic therapy and heat. Whether a cell is undergoing apoptosis is currently determined by taking samples of cells or tissues of interest and observing, using histological and DNA measurement methods, whether the cells exhibit the morphological changes that are indicative of apoptosis. These changes include membrane blebbing, DNA condensation and DNA fragmentation. These methods, however, are not only invasive, but are also time-consuming, requiring processing of a cell or tissue sample before data relating to apoptosis can be obtained.
The ability to differentiate apoptotic cells or otherwise dead or dying cells from living cells non-invasively, in vitro, and in vivo at both superficial and deep sites, would potentiate clinical diagnoses and provide a more efficient way of studying apoptotic or non-apoptotic cell death and evaluating the clinical response of a subject to a therapeutic agent or regimen.